FORMATION OF CARBOXYLIC-ACIDS FROM ALCOHOLS AND OLEFINS IN ZEOLITE H-ZSM-5 UNDER MILD CONDITIONS VIA TRAPPING OF ALKYL CARBENIUM IONS WITH CARBON-MONOXIDE - AN IN-SITU C-13 SOLID-STATE NMR-STUDY

Using in situ C-13 solid State MAS NMR (for some reagents in combinati on with ex situ CC-MS), it is shown that butyl alcohols and olefins (e thene, isobutene, octene-1) undergo carbonylation to form carboxylic a cids (the Koch reaction) with high conversion on zeolite H-ZSM-5 at 29 6-373 K. The reactions proceed without application of pressurized cond itions, just upon coadsorption of CO and alcohols or CO, H2O, and olef ins on zeolite. The observed Koch reaction under mild conditions provi des strong evidence for the formation of alkyl carbenium ions from alc ohols and olefins on the zeolites as crucial reaction intermediates. O f the family of carbenium ions, CO reacts selectively with tertiary ca tions to produce tertiary carboxylic acids, unless the carbonylated mo lecule is too large for more bulky tertiary moieties to be accommodate d and carbonylated in the narrow pores of H-ZSM-5. Thus, t-BuOH, i-BuO H, and isobutene produce trimethylacetic acid with high selectivity an d conversion, while ethene transforms selectively into 2-methyI-2-ethy l butyric acid. Reaction of octene-1 molecules with CO and H2O results in acids of the C8H17COOH and C16H33COOH families with predominantly linear hydrocarbon chains. The data obtained may open up new possibili ties in using solid acids in organic synthesis as carbonylation cataly sts under mild conditions, i.e., low temperature and normal atmospheri c pressure. (C) 1996 Academic Press, Inc.